Proposed method of DMSP cleavage into DMS via DddQ lyase

Dimethylsulfide (DMS) is a gas that plays a key role in the global biogeochemical sulphur cycle. Synthesis of this gas is due to breakdown of dimethylsulfoniopropionate (DMSP) by specialised lyases which can be released via turbulence, grazing or viral lysis. Approximately 300 Tg of DMS is created and 10% of this is transferred to the atmosphere via ocean microbial processes. The authors state the importance of DMS in its influence on global weather patterns. DMSO (a form of oxidised DMS) can form cloud condensation nuclei’s (CCN’s) which are tiny hygroscopic particles on which water vapour can condense and cause formation of a cloud. DMSO can also affect cloud reflectivity resulting in a decreased amount of damaging solar radiation. With more reflected energy, this would decrease the global mean temperature. Could altering these interactions result in some control over the amount of exposure from this damaging energy? 

This paper explores the crystal structure of a DddQ lyase extracted from Ruegeria lacuscaerulensis ITI_1157 and the molecular mechanism of the catalytic effect it has on the cleavage of DMSP into DMS. This was achieved via structural analyses, molecular dynamics simulations and mutational assays.

In terms of structure, the authors ascertained that DddQ lyase folds into a β-barrel structure and contains six hydrophilic residues, essential to catalysis. To determine their importance, site-directed mutations were created; Tyr120Ala, His123Ala, His125Ala, Glu129Ala, Glu129Gln, and His163Ala. They discovered that these mutations inhibited the ability of DddQ towards DMSP therefore confirming the key role these residues play in DMSP cleavage. The mechanism they proposed is thus; DMSP enters the DddQ active site and oxygen from DMSP binds to Zn²⁺ ion, replacing Tyr131 (one of the six highly conserved hydrophilic residues in DddQ lyase) and resulting in a β-elimination reaction.

This paper is of high interest especially in the dynamic global climate. By exploring the key processes that affect the cleavage of DMSP into DMS and the role this biogenic gas plays, therein lies a greater ability to reveal its interactions with the environment.

Li C., Wei, T., Zhang, X., Gao, X., Wang, P., Xie, B., Su, H., Qin, Q., Zhang, X., Yu, J., Zhang, H., Zhou, B., Yang, G. & Zhang, Y. (2013). Molecular insight into bacterial cleavage of oceanic dimethylsulfoniopropionate into dimethyl sulfide. PNAS. 111 (3), 1026–1031. doi: 10.1073/pnas.1312354111